Oh, dear. Focal length is focal length. Extension is extension. You don't need no steenkin' crop factors. Put the idea out of your mind.
Now, about the little Shen Hao. Cute little camera.
The manufacturer's spec sheet (http://www.shen-hao.com/PRODUCTSabout.aspx?i=933&id=n3) says that minimum extension is 52 mm, maximum is 190 mm. Any lens with a flange-focal distance no shorter than 52 mm and no longer than 190 mm (but read on about longer lenses) can be used on the camera. 47/5.6 SA XL and 45/4.5 Apo Grandagon both have flange-focal distances > 52.0 mm, are probably the shortest lenses you can use. A plain 47/5.6 SA "multicoating" in #0 should just make it. My older 47/5.6 SA in #00 won't quite. At the long end, if you want to get reasonably close (1:10) the longest lens that will work without heroic measures (extension tube between shutter and board, "top hat" board) is around 170 mm. A lens with 190 mm flange-focal distance will just focus to infinity, and no closer, on the little Shen.
I shoot 2x3 with, mainly, Graphics. No movements to speak of. I also have a 2x3 Cambo monorail, prefer the Graphics. You can read about how I've used them at http://www.galerie-photo.com/telecha...2011-03-29.pdf If you need movements, a Graphic is not for you.
ic, the normal focal length (= format's diagonal) for 2x3 is 100 mm. To my way of thinking, 180 is more than slightly long. I'm a little surprised that it doesn't offer double extension, I've always thought that was the norm. Oh, well.